The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2001-106292 filed Apr. 4, 2001, which is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a cleaning unit for removing remaining toner, paper powder, etc., from the surfaces of a photoconductor drum, an intermediate transfer body, and the like after a toner image is transferred to record paper in an image formation apparatus such as an electrophotographic copier or a laser beam printer and more particularly to improvements for miniaturizing an image formation apparatus and saving energy.
2. Description of the Related Art
Generally, an image formation apparatus such as an electrophotographic copier or a laser beam printer forms a toner image on the surface of a photoconductor drum in response to image data and then transfers the toner image to a record sheet and fuses the transferred toner image on the record sheet, thereby providing a record image. It has also been known that some recent full color copiers or full color laser beam printers primarily transfer a toner image formed on a photoconductor drum to an intermediate transfer body, superpose four color toner images of yellow, cyan, magenta, and black on the intermediate transfer body, and secondarily transfer the resultant toner image to a record sheet in batch, thereby forming a full color record image.
Since the toner image transfer efficiency is affected by fluctuations of the resistance values of the record sheet and the intermediate transfer body accompanying change in the surface state, temperature, or humidity of each of the photoconductor drum and the intermediate transfer body, it is difficult to maintain the toner image transfer efficiency 100%, and the remaining toner is deposited on the surfaces of the photoconductor drum and the intermediate transfer body of the toner image transfer sources still after the toner image is transferred. Thus, hitherto, an image carrying body such as the photoconductor drum or the intermediate transfer body has been provided with a cleaning unit downstream from the toner image transfer part for removing the remaining toner on the image carrying body before another toner image is formed.
As such a cleaning unit, a unit for pressing an elastic rubber blade against the surface of a photoconductor body and removing the remaining toner by a mechanical force is used widely. The blade-type cleaning unit has the advantages that it is mechanically simple and is at low cost because it does not require a drive section. However, the rubber blade not only removes the remaining toner, but also shaves little by little the surface of the image carrying body to be cleaned and thus the blade-type cleaning unit has the disadvantage that damage to the photoconductive layer, etc., of the photoconductor drum is large, shortening the life of the photoconductor drum. Particularly, in recent years, making small the diameter of the photoconductor drum has been noticeable from the viewpoint of miniaturization and there has also been a trend toward an increase in the number of revolutions of the photoconductor drum for the same number of print sheets. Thus, with the blade-type cleaning unit, the life of the photoconductor drum would be shortened more and more.
On the other hand, known as any other cleaning unit than the blade-type cleaning unit is a fur brush cleaning unit for bringing a brush roll with a myriad of slidingly scrubbing bristles planted into contact with an image carrying body and rotating the brush roll at high speed, thereby mechanically removing the remaining toner. Such a brush roll is rotated by a motor and the toner capture efficiency can be raised by setting large the linear speed ratio of the brush roll to the image carrying body to be cleaned. With the fur brush cleaning unit, as compared with the blade-type cleaning unit, damage to the image carrying body is small and it can be expected that the life of the photoconductor drum will be prolonged accordingly. However, to rotate the brush roll, a motor and a gear train become necessary and the configuration of the cleaning unit must be enlarged.
In recent years, miniaturization of image formation apparatus has been advancing remarkably and making small the diameter of the image carrying body such as the photoconductor drum or the intermediate transfer body has been noticeable. Thus, it is desirable that the cleaning unit should be easy on the surface of the image carrying body and should make it possible to prolong the life of the image carrying body. From the viewpoints of miniaturization and energy saving of image formation apparatus, a cleaning unit not requiring drive means of a motor, etc., is desired. Particularly, the need for such a cleaning unit is large with a tandem-type full color copier or full color printer comprising photoconductor drums in a one-to-one correspondence with toner colors.
It is therefore an object of the invention to provide a cleaning unit that can exert sufficient toner capture performance without having a drive mechanism such as a motor, can contribute to miniaturization and cost reduction of an image formation apparatus, and makes it possible to lessen damage to an image carrying body for prolonging the life of the image carrying body.
From the viewpoint of lessening the stress that a rotation body such as a photoconductor drum or an intermediate transfer body receives as a brush roll slidingly scrubs the rotation body, it may be possible to allow the brush roll to rotate simply to follow rotation of the rotation body without rotating the brush roll by a drive source such as a motor. If the brush roll is thus rotated with rotation of the rotation body, slidingly scrubbing the surface layer of the rotation body by an external force of a motor, etc., is avoided and thus damage to the surface layer can be prevented as much as possible and it can be expected that the life of the rotation body will be prolonged. Since the motor and gear train for driving the brush roll become unnecessary, the structure becomes simple and compact and the manufacturing cost can also be reduced.
However, to efficiently capture the toner deposited on the rotation body in the brush roll, the shearing force for moving the toner from the surface of the rotation body is required. As the brush roll is allowed simply to rotate with rotation of the rotation body, the linear speed of the brush roll and that of the rotation body become roughly the same at the contact position between the brush roll and the rotation body and thus a sufficient shearing force cannot be made to act on the toner.
Then, in the invention, the tips of slidingly scrubbing bristles of the brush roll for slidingly scrubbing the rotation body are inclined in the circumferential direction, whereby the linear speed of the brush roll rotated with rotation of the rotation body is controlled aggressively.
According to the invention, there is provided a cleaning unit having a brush roll having a large number of slidingly scrubbing bristles upright in relation to a rotation shaft thereof, the brush for slidingly scrubbing a surface of a rotation body with the brush roll to remove a toner deposited on the rotation body. When the brush roll is out of contact with the rotation body, tips of the slidingly scrubbing bristles are inclined in a circumferential direction thereof. When the brush roll is in contact with the rotation body, the brush roll does not drive to rotate itself and is rotated to follow rotation of the rotation body. The linear speed of the brush roll at a contact position between the brush roll and the rotation body is different from that of the rotation body at the contact position.
According to the technical means, when the brush roll is not contact with the rotation body, the tips of the slidingly scrubbing bristles are inclined in the circumferential direction. Thus, if the brush roll is placed in contact with the rotation body and the rotation body is rotated, it is made possible to control as desired to some extent the linear speed of the brush roll rotated with rotation of the rotation body in response to the inclination direction, the inclination angle, the length, the hardness, etc., of the slidingly scrubbing bristles, and the linear speed of the brush roll can be made different from that of the rotation body. Consequently, the shearing force can be made to act on the toner deposited on the rotation body and it is made possible even for the brush roll rotated simply with rotation of the rotation body to capture the toner efficiently.
If the outer diameter of the brush roll is the same, the length of the slidingly scrubbing bristles can be set longer as the tips of the slidingly scrubbing bristles are inclined, so that it is also made possible to increase the amount of toner that can captured and held in the brush roll.
In the invention, the tips of the slidingly scrubbing bristles of the brush roll may be inclined in any circumferential direction. To incline the tips of the slidingly scrubbing bristles along the rotation direction of the rotation body, the peripheral speed of the brush roll tends to become lower than the peripheral speed of the rotation body; to incline the tips of the slidingly scrubbing bristles in the opposite direction to the rotation direction of the rotation body, the peripheral speed of the brush roll tends to become higher than the peripheral speed of the rotation body.
The inventors recognized that if the linear speed ratio of the brush roll to the rotation body is 0.6 or less or 1.3 or more, the toner deposited on the rotation body can be captured effectively and the remaining toner deposited on the rotation body does not adversely affect the image formation operation.
The outer diameter of the brush roll, the length and the hardness of the slidingly scrubbing bristles, and the surface hardness and the surface roughness of the rotation body can be named as factors affecting the rotation speed of the brush roll rotated with rotation of the rotation body. These are selected appropriately, whereby the linear speed ratio of the brush roll to the rotation body can be adjusted as desired.
Only the tips of the slidingly scrubbing bristles may be inclined in the circumferential direction of the brush roll, but may be made upright in relation to the rotation shaft in an inclined state from the root. In the former case, the brush roll can be manufactured by making slidingly scrubbing bristles upright roughly perpendicularly in relation to the periphery of a rotation shaft and then laying down only the tips of the slidingly scrubbing bristles in a specific direction while heat is applied. On the other hand, in the latter case, the brush roll can be manufactured by winding a cloth with slidingly scrubbing bristles upright in an inclined state around a rotation shaft.
To capture toner from the rotation body into the brush roll, only the shearing force acting based on the linear speed difference between the rotation body and the brush roll may be used. However, the brush roll may be made up of a conductive rotation shaft and slidingly scrubbing bristles and a cleaning bias may be applied between the brush roll and the rotation body. In doing so, the toner deposited on the rotation body can be captured in the brush roll more effectively. The voltage polarity of the cleaning bias may be selected appropriately in response to the charge polarity of the toner to be captured. For example, if toner charged to the negative polarity is used to form a toner image, the toner of the negative polarity remains on the photoconductor drum and the intermediate transfer body after the toner image is transferred. The cleaning bias of the positive polarity is applied to the brush roll, whereby the remaining toner can be captured. Some remaining toner is reversed to the positive polarity by a transfer current. Thus, if the toner reversed in polarity is captured, the cleaning bias of the negative polarity is applied to the brush roll. The inventors recognized that if the cleaning bias is applied to the brush roll, the linear speed of the brush roll tends to rise 5%.
The photoconductor drum, the intermediate transfer drum as described above, a photoconductor belt, and an intermediate transfer belt can be named as the rotation bodies to which the cleaning unit of the invention is applied. In recent years, a transfer roll to which a transfer bias is applied has been used to transfer a toner image to a record sheet; toner from a photoconductor drum or an intermediate transfer drum also tends to be deposited on the transfer roll. Therefore, the cleaning unit of the invention can also be applied to the transfer roll.